Cristiano Ronaldo's late goal helped Juventus to maintain their perfect start to the Serie A season with a hard-fought 2-0 victory away to Frosinone.

Massimiliano Allegri's Juventus, who are chasing an eighth consecutive Italian league title, have now won their opening five league games for the third time in five seasons.

Ronaldo was the hero, days after being sent off on his Champions League debut for the Turin club, breaking the deadlock from close range in the 81st minute to take his Serie A tally to three goals in five games.

The well-drilled hosts, who have picked up just one point this season and are still waiting to score their first goal, provided a surprisingly stern test for the champions but their challenge ended in stoppage time when Federico Bernardeschi finished off a counter attack to put the result beyond doubt.

"We expected it to be like this," Allegri told reporters. "Frosinone had conceded five to Sampdoria and we played down to 10 men for 70 minutes against Valencia [in the Champions League] on Wednesday.

"We just needed to have patience and after many shots, crosses and passes, we found the breakthrough."

Juve lead the Serie A standings with a maximum 15 points from their opening five games.

In other Serie A action, Roma coach Eusebio di Francesco's position is under increasing scrutiny after his side's shock 2-0 defeat by Bologna which club president James Pallotta said made him feel "disgusted".

Bologna went into the game without a win or a goal to their name this season but strikes from Federico Mattiello and Federico Santander gave Pippo Inzaghi's side their first home win against the capital club since 2004 and left Roma in 14th place with five points.

"If something doesn't snap inside the players, then we're going to struggle," said Di Francesco.

"We could just sit there in front of the goal and hope the right cross comes in but that is not my philosophy of football."

Napoli continue to look like Juventus's most likely challengers after beating Torino 3-1 thanks to a Lorenzo Insigne double and a Simone Verdi strike.

Carlo Ancelotti's side have won four of their five Serie A games so far and occupy second place, three points behind the leaders.

Atalanta scored a stoppage-time equaliser to earn a 2-2 draw with AC Milan at San Siro, Lazio moved into fifth place with a 4-1 win at home to Genoa and Chievo remain bottom of the pile after falling to a 2-0 home defeat to Udinese.